Data offload generally refers to a transfer process of data that is temporally stored on a physical medium, such as a Network video recorder, to a desired destination upon detecting a suitable connection for the data transfer. The offload can be carried out wirelessly or with wired connection. The use of complementary or dedicated technology for the data offload purposes is especially advantageous in a situation where the data network resource allocated for the data delivery is about to reach its maximum capacity.
A specific challenge in wireless data traffic is the data delivery to and from mobile vehicles, especially public transportation vehicles, like trains, trams, metro trains and busses. A moving vehicle, as such, poses challenges to reliable data transfer, where the usable data rate typically reduces as a function of the speed of the vehicle. Many public transportation operators have started to offer a wireless data connection, such as a Wi-Fi connection, for the passengers to use during their trip. Moreover, the requirements for using video surveillance in public transportation vehicles are continuously increasing. The video data from a plurality of surveillance cameras, i.e. CCTV data, together with the data traffic of the passengers, easily amounts to an extensive quantity of data, which cannot be transferred within the capacity of current wireless networks without a significant delay.
Moreover, governmental regulations for keeping the CCTV data stored for a certain period, such as 14 days, pose challenges to both storing the data onboard and also carrying out wireless data offload efficiently, when the vehicle stops e.g. at a train station or a bus stop. The amount of data to be offloaded may be very large and a public transportation vehicle typically stops only for a short period. If the wireless offload is not successful or sufficiently comprehensive when stopped, the amount of non-offloaded CCTV data at the vehicle grows and may exceed the storage capacity of a network recorder of the vehicle. The problem becomes even more severe at long distance travels having stations or stops very sparsely.